1. Field of the Invention
The present invention relates to a device for aiding the piloting of an aircraft, especially a rotary-wing aircraft and in particular a helicopter.
More precisely, it relates to a device making it possible to present information cues to a pilot of the aircraft, which are capable of providing the latter with indications regarding the exact position of said aircraft with respect to the surrounding space, especially in poor visibility, or even in the complete absence of visibility. Such cues are generally very useful, or even indispensable, when approaching a landing strip.
2. Description of Related Art
On aeroplanes, especially civil transport aeroplanes, a device for presenting cues of this type is known, and is associated with a guidance beam or axis (for example of the "ILS" type) transmitted from the ground in proximity to a landing strip and which is intended to guide the aeroplane during the approach to the strip, with a view to landing.
To this end, the known device provides the pilot(s) with two cues presented on a display screen, namely:
a first cue ("LOC") comprising an arrow which the pilot must orient in terms of heading on the guidance axis and a deviation bar, whose lateral displacement on the screen with respect to the arrow is representative of the offset between the guidance beam and the position of the aircraft; and PA1 a second cue ("GLIDE") which indicates the relative vertical position between said guidance axis and the position of the aircraft. PA1 an approach at gentle slope, around 3.degree., is not well suited to the deployment capabilities of helicopters; and PA1 helicopters must be able to land on unprepared zones which are not furnished with guidance beams. PA1 first means for determining the slope and the heading of a flight path which said aircraft can take in order to join up with a preset path; and PA1 second means for presenting, on a display screen, a second characteristic sign, whose position on said display screen is representative both of the slope and of the heading of said flight path, PA1 according to a first direction representing the heading, on the distance in a horizontal plane between the position of the aircraft and said preset path; and PA1 according to a second direction representing the slope, on the distance in a vertical plane between the position of the aircraft and said preset path. PA1 the discrepancy in slope p and the discrepancy in heading r between said preset and flight paths satisfy the following relations which depend on the distances dv and dh in meters m respectively in the vertical plane and the horizontal plane between the position of the aircraft (H) and said preset path (T): PA1 when the preset path comprises a plurality of successive segments, the current segment, used to determine the slope and the heading of said preset path, is advantageously the one which is closest to the position of the aircraft. PA1 a third characteristic sign, for example in the form of straight lines, linking together said first and second characteristic signs, thus making it possible to depict to the pilot the limits of the aerial course which he must follow in order to join up with said preset path and therefore eases the understanding and evaluation of the various cues presented; and/or PA1 a fourth characteristic sign indicating the direction in which the aircraft is flying, thereby easing and simplifying the piloting since it is then sufficient for the pilot to direct the aircraft so that said fourth characteristic sign is and remains superimposed on said second characteristic sign indicating the advised flight path; and/or PA1 a fifth characteristic sign indicating the direction of a point in space which will be reached by said aircraft within a specified duration, thus making it possible to join up with the preset path within said specified duration if the pilot carries out a piloting making it possible to superimpose this fifth characteristic sign on said second characteristic sign. PA1 at least one auxiliary sign which is intended to deputize for a characteristic sign which has exited the field of view represented on said display screen and which is situated, according to a field exit direction, at a predetermined distance from the actual position of said exited characteristic sign; and/or PA1 a first additional sign warning of a modification, within a predetermined duration, of the preset path, for example a change of heading and/or of slope. This first additional sign disappears when said first characteristic sign is superimposed thereon, that is to say when the path modification has been made; and/or PA1 a second additional sign indicating the position of the ground relative to a zone in space connected with said aircraft. This second additional sign is preferable associated with the fourth characteristic sign indicating the direction in which the aircraft is flying.
These cues relate to values which are proportional to the angle between said guidance axis and the line of aim of the point at which the aircraft expects to touch down.
Such a known device for presenting cues is well suited to an approach made in a straight manner, with a fixed and relatively gentle slope, for example 3.degree., as is generally the case for an aeroplane.
However, when the approach has to be made according to a preset path which exhibits several successive segments exhibiting different headings and slopes, as well as relatively large values of slope of up to 15.degree., as may be the case for a helicopter, the aforesaid cues are not appropriate and are moreover inadequate.
This is because a cue in angular form obliges the pilot to pass through a particular point in space. Now, such a constraint is not useful in respect of the various points of transition of a path having a plurality of segments, with the exception of the last segment terminating in the landing strip.
Moreover:
Consequently, the known and aforesaid device is not satisfactory for guidance along complex preset paths.
The document FR-2 666 428 describes a process for displaying pilot-aid symbols on a screen aboard an aircraft. This known document teaches in particular the displaying, according to a three-dimensional representation, of the approach segments situated on the path which the aeroplane must travel. To this end, the current segment of travel, as well as the next segment, are displayed respectively according to two parallelepipeds, in perspective.
Furthermore, the document FR-2 752 051 discloses a device for assisting the guidance of a vehicle over a path. This known device comprises means for determining the slope and the heading of a flight path which the vehicle can take in order to join up with a preset path and means for displaying a guidance window, into which must be brought and wherein must be maintained a symbol representing the speed vector of the aeroplane, during the guidance of the aeroplane. This guidance window is centered on a preset point which represents the direction of guidance to be followed by the aircraft, in terms of heading and slope. The coordinates of this preset point are defined by the point of intersection between a sphere (of fixed radius) centered on the position of the aeroplane and the preset path.
However, the pilot has no information regarding the discrepancies of slope and of heading between the preset and flight paths, and this may be very detrimental in certain flight conditions.